Hitherto, polyimide resins having all of excellent heat resistance, electric characteristics and mechanical characteristics have been used for passivation films, surface protective films and layer insulation films in insulation materials of electronic parts and semiconductor devices. Of these polyimide resins, in the case of those which are used in the form of negative type photosensitive polyimide precursor compositions, heat resistant relief pattern films can be easily formed by coating them and subjecting the coating to exposure, development and hot imidation. Such negative type photosensitive polyimide precursor compositions have the advantage that the steps involved can be considerably shortened as compared with when conventional non-sensitive polyimides are used.
However, when the above negative type photosensitive polyimide precursor compositions are used, it is necessary to use organic solvents such as pyrrolidones and ketones in a large amount as developers in the developing step, and it is required not to use organic solvents from the points of view of safety and recent growing interest in environmental protection. Under the circumstances, various proposals for heat resistant photosensitive resin materials which can be developed with a dilute aqueous alkali solution, as well as photo resists, have recently been made in the above-mentioned fields of materials.
Among them, the utilization of a hydroxypolyamide soluble in an aqueous alkali solution, for example, polybenzoxazole precursors, has recently been made. As these methods, there are known a method of using a positive type photosensitive material formed by mixing a polybenzoxazole precursor and a photoactive component such as quinonediazide (JP-B-1-46862, JP-A-63-96162, etc.), a method of using a negative type photosensitive material prepared by introducing a photopolymerizable unsaturated double bond-containing group into a part of phenolic hydroxyl groups of a polybenzoxazole precursor, followed by mixing with a monomer having a photopolymerizable unsaturated double bond, a photopolymerization initiator and the like (JP-A-2002-12665), and others.
In the case of a negative type photosensitive material, a resin having a photopolymerizable unsaturated double bond or the like is polymerized by irradiation with light and as a result, becomes insoluble in the developer. On the other hand, in the case of a positive type photosensitive material, a resin which is lower in solubility in the developer due to the interaction with a mixed photoactive component becomes soluble in the developer due to the decomposition of the photoactive component caused by irradiation with light. Therefore, when a resin is used as a negative type photosensitive material, in which the difference in solubility in the developer between the light irradiated part and the light non-irradiated part can be made greater, process margins can be made much broader than when it is used as a positive photosensitive material, and hence the relief pattern can be easily formed after development. Moreover, in general, the negative photosensitive materials are higher than the positive photosensitive materials in the storage stability of the composition.
Furthermore, since a polybenzoxazole film has similar thermosetting characteristics to those of a polyimide film, a negative type photosensitive polybenzoxazole precursor which can be developed with a dilute aqueous alkali solution is expected to be a promising substitute material for a organic solvent developing type negative type photosensitive polyimide precursor.
On the other hand, there are various changes in the method of packaging a semiconductor device in which the above materials are used. Recently, from the viewpoints of improvement of integration and function, and miniaturization of chip size, there is a marked tendency to use a multilayer interconnection package, and the conditions to which the polyimide film or polybenzoxazole film is exposed during the process of formation of the structures are further diversified. Therefore, the semiconductor materials are required to have higher chemical resistance to strong acids and strong bases.
Moreover, for the same reasons, the method for mounting semiconductor devices on print wiring substrates is changing from the conventional mounting method using a metal pin and a lead-tin eutectic solder to the methods in which a polyimide film or polybenzoxazole film of the semiconductor devices directly contacts with solder bumps, such as BGA (ball grid array) and CSP (chip size packaging) according to which a higher density mounting can be attained. The solders used are also being changed to those of high melting point free from lead for the purpose of reduction of environmental load, and furthermore the solders for bumps are generally those which are further higher in melting point than those for mounting on substrates.
That is, the polyimide films or polybenzoxazole films of semiconductor devices are exposed to unexpectedly high temperatures while contacting with flux at the reflow step of solder bumps, and hence they are required to have higher heat resistance and high-temperature flux resistance.
An object of the present invention is to provide a method for forming on a substrate a relief pattern having conspicuously high heat resistance and chemical resistance after curing with heating and a negative type photosensitive resin composition of high efficiency used for the above method. Another object is to provide a method for producing semiconductor devices using the above method or the above negative type photosensitive resin composition.